The present invention relates to an extreme ultraviolet light source device, a laser light source device for an extreme ultraviolet light source device, and a method of adjusting a laser light source device for an extreme ultraviolet light source device.
A semiconductor chip is created, for example, by reduction projection of a mask on which a circuit pattern is drawn onto a wafer having a resist applied thereon, and by repeatedly performing processing, such as etching and of thin film formation. The progressive reduction of the scale of semiconductor processing demands the use of radiation of further short wavelength.
Accordingly, research has been made on a semiconductor exposure technique which uses radiation of extremely short wavelength of 13.5 nm or so and a reduction optics system. This type of technique is termed EUVL (Extreme Ultra Violet Lithography: exposure using extreme ultraviolet light). Hereinafter, extreme ultraviolet light will be abbreviated as “EUV light”.
Three types of EUV light sources are known: an LPP (Laser Produced Plasma: plasma produced by a laser) type light source, a DPP (Discharge Produced Plasma) type light source, and an SR (Synchrotron Radiation) type light source.
The LPP type light source is a light source which generates a plasma by irradiating laser beam on a target material, and employs EUV radiation emitted from this plasma. The DPP type light source is a light source which employs a plasma generated by an electrical discharge. The SR (synchrotron radiation) is a light source which uses orbital radiation. Of those three types of light sources, the LPP type light source is more likely to acquire high-output EUV radiation as compared to the other two types because the LPP type light source can provide an increased plasma density, and can ensure a larger solid angle over which the radiation is collected.
To acquire high-power laser beam at a high repeating frequency, therefore, a laser light source device configured according to the MOPA (Master Oscillator Power Amplifier) system is proposed (JP-A-2006-128157).
An art of regulating the wave front of laser beam using a deformable mirror whose surface shape can be variable controlled freely to some extent is known (JP-A-2003-270551).
To acquire EUV radiation of 100 W to 200 W or so, for example, it is necessary to set the output of a carbon dioxide gas laser as driver laser beam to 10 to 20 kW or so. The use of such high-power laser beam causes various optical elements in the optical path to absorb radiation and thus become hot, so that the shape and direction of the wave front of laser beam change. It is described herein that the wave front of laser beam includes the shape and direction of the wave front of laser beam.
When high-power laser beam passes through a lens or a window, the shape and refractive index of the lens or window vary due to a heat-originated temperature increase, changing the wave front of laser beam. When the wave front of laser beam changes, for example, the laser beam cannot be efficiently input to an amplification area in a laser amplifier, so that a laser output cannot be acquired as expected. Further, because the focal position of laser beam which is input into the chamber changes according to a change in the wave front of the laser beam, the laser beam cannot be efficiently irradiated on a target material, thus lowering the power of the EUV radiation.